Abstract We propose a new method to measure eccentricity of the annulus in real-time during primary cementing. Our methodology is based on seeding the displacing fluids with neutrally buoyant particles. The process of seeding can happen by a specially designed bottom plug that releases a particle every few seconds. Particles at different azimuthal position experience a different axial velocity, because of the eccentricity of annulus. We infer the local velocity of the fluids by tracking the trajectories of particles and correlate it to the local eccentricity of the annulus. We show that this methodology allows us to find an axial profile of eccentricity along the well, and helps to identify geometrical irregularities, such as washouts, along the annulus.

Abstract The primary goal of the oil and gas well cementing is zonal isolation. During the production life of a well, the cement experiences various severe conditions affecting its permeability. These conditions include cracking, debonding, and shear failure which can be worsened by pressure fluctuations during hydraulic fracturing operations. Any of these conditions by forming micro-cracks within the cement or micro-annuli at the casing/cement or cement/rock interfaces create cement permeabilities far beyond the intrinsic permeability of the intact cement sheath. Recently, some studies have been devoted to improving the overall mechanical behavior of the cement by adding carbon nanotubes and carbon nano-fibers. Although these nano-additives offer considerably high strength and modulus, the high costs of these materials persuade us to find alternatives at relatively low costs, such as, graphite nanoplatelets (GNPs). Our preliminary laboratory studies show the effectiveness of GNPs in the enhancement of durability characteristics of the prepared nanocomposite cement paste by improving its compressive strength, ductility and toughness resistance. Considering the importance of dispersion of nanoadditives within the cementitious matrix, we physically or chemically manipulate the surface properties of GNPs to prevent the agglomeration of nanoparticles.

Abstract Wells are essential in oil and gas production and construction of them is one of the main cost drivers for field development. It is normally needed to drill and construct new wells from existing fields during most of the production time. In order to reduce costs one can re-use parts of existing wells when they are no longer efficient. This is done in offshore fields also when there is limitation for new wells due to capacity of the subsea template. Through tubing drilling is a method to drill a side track through the wellbore tubulars. However, this will normally result in a smaller and less effective well completion. Removing parts of the casing section and drill a larger size sidetrack is an option to provide a new full-size wellbore. Removing the 9 5/8” casing through the settled particle in the annulus can be challenging. The wellbore annulus is normally filled with old drilling fluid, displacing fluid and/or cement slurry. The solid particles of these annular fluids are settled during years of shut-in and make it difficult to move the casing sections. There are several techniques for pulling the casing section, but there is a lack of knowledge of some of the key mechanism causing the resistance in these operations. In order to study and address the dominating effects in these operations, down-scaled laboratory tests are performed. The experiments reported here are performed by pulling steel pipes through the settled barite in the annulus. The pipes used in the tests are down-scaled from typical casing sizes with and without collars. The barite slurry compacted inside the annulus have different hydrostatic and pore pressures. When the pipe is pulled the required mechanical force is measured. Results show that the single most significant factor causing resistance when pulling the tubulars is the collars outside the pipe. Furthermore, it is identified that the pore pressure improves the mobility of the settled particle around the collar. In total these results provide improved understanding on the dominating factors during pulling pipes from a packed annulus.

Abstract Cementing operations in deepwater exhibit many challenges worldwide due to shallow flows. Cement sheath integrity and durability play key roles in the oil and gas industry, particularly during drilling and completion stages. Cement sealability serves in maintaining the well integrity by preventing fluid migration to surface and adjacent formations. Failure of cement to seal the annulus can lead to serious dilemmas that may result in loss of well integrity. Gas migration through cemented annulus has been a major issue in the oil and gas industry for decades. Anti-gas migration additives are usually mixed with the cement slurry to combat and prevent gas migration. In fact, these additives enhance and improve the cement sealability, bonding, and serve in preventing microannuli evolution. Cement sealability can be assessed and evaluated by their ability to seal and prevent any leakage through and around the cemented annulus. Few laboratory studies have been conducted to evaluate the sealability of oil well cement. In this study, a setup was built to simulate the gas migration through and around the cement. A series of experiments were conducted on these setups to examine the cement sealability of neat Class H cement and also to evaluate the effect of anti-gas migration additives on the cement sealability. Different additives were used in this setup such as microsilica, fly ash, nanomaterials and latex. Experiments conducted in this work revealed that the cement (without anti-gas migration additive) lack the ability to seal the annulus. Cement slurries prepared with latex improved the cement sealability and mitigated gas migration for a longer time compared to the other slurries. The cement slurry formulated with a commercial additive completely prevented gas migration and proved to be a gas tight. Also, it was found that slurries with short gas transit times have a decent potential to mitigate gas migration, and this depends on the additives used to prepare the cement slurry.

Abstract As China’s offshore drilling and production projects gradually march into the deep water, the requirements for scientific and technological progress are imminent. The occurrence of the 2010 Macondo disaster has presented a serious challenge to the safety of deepwater in technology. The deepwater wellbore consists of several layers/channel barriers, which constitute the wellbore barrier system and have a complicated structure. With the increase of water depth and well depth, the temperature of oil and gas produced at the wellhead is getting higher and higher, and the fluid in the annulus of the casing is heated by the conduction and convection of fluids such as oil and gas produced in the high temperature formation. Up to 60 degrees Celsius, the thermal expansion of the annulus fluid can cause the casing to burst, which can cause significant loss of personnel and property. Therefore, accurate temperature calculation of deep water wellbore is the key to the calculation of trap pressure prediction. The calculation of the wellbore temperature is affected by the oil casing and the thermophysical parameters such as the size of the wellbore, fluid composition, flow regime, casing and cementing sheave. By appropriately simplifying the model and sensitivity analysis, it is found out the dominant factors which affect the temperature profile.

Abstract Casing strings and liners are important subsurface structural components in petroleum and in geothermal wells. After the casing string has been run in hole, it is cemented to the formation by pumping a sequence of spacer fluids and cement slurry into the annulus outside the string. Spacer fluids are usually pumped ahead of the cement slurry in order to displace the drilling fluid from the annulus that is to be cemented, and thereby avoid contamination of the cement slurry. Fluid displacements are governed by inertia, buoyancy and viscosity effects, in addition to being strongly influenced by the annular geometry. Poor centralization of the casing or irregularities such as washouts can influence the displacement flows both locally and over long axial distances. We present three dimensional numerical simulations of the displacement flow involving two viscoplastic fluids in the vicinity of a symmetric local hole enlargement. We focus on laminar flow regimes in the regular part of the annulus and investigate how the volumetric flow rate and the mass density difference between the fluids affect the displacement efficiency in the regular and the irregular parts of the annulus. This study considers viscoplastic displacement flows in a near-vertical, irregular annulus and is an extension of a previous publication that focused on a near-horizontal annulus. We contextualize our simulations by comparison to industry guidelines for effective and steady laminar displacements in the regular, near-vertical annulus. Here, eccentricity favors flow in the wider sector of the annulus while a positive density difference between the fluids generates secondary, azimuthal flow toward the narrow side of the annulus. In the enlarged and irregular section, both the axial bulk velocity and casing eccentricity decrease sharply and buoyancy becomes more pronounced compared to in the regular annulus. We quantify and discuss the effects of local hole enlargements on displacement efficiencies. Simulations of cementing flows can aid in optimizing fluid properties and pump rates, including when the wellbore has suspected or confirmed zones of irregular geometries.

Abstract The determination of the slip velocity, or whether a solid particle will sediment, during its transport is of prime importance for hole cleaning evaluations during drilling operations. Yet, this task is complexified by the asymmetry of the annulus when the central pipe axis does not coincide with the borehole central line and when the inner string rotates, especially since drilling fluids typically follow a yield stress power law rheological behavior. This paper describes the modelling of the movement of a particle in such conditions yet with the following simplifications: the inner tube is eccentric but has a uniform movement, the shape of the particle is assimilated to a prolate, the change of shear rates in the fluid around the slipping particle is neglected and collisions between particles are not considered. Otherwise, gravitational effects are incorporated by accounting for the mass density difference between the particle and the surrounding fluid mixture and by considering the borehole inclination. The particle spin is also estimated as it plays an important role in the determination of the drag and lift forces. The solution to the differential equations that describe the time evolution of the position and orientation of the particle, depend largely upon the initial conditions. Therefore, an ensemble of boundary conditions is generated at a starting cross-section along the annulus and the resulting particle trajectories are estimated. It is then possible to estimate a probabilistic slip velocity for particles of the considered dimensions, far away from the entrance region. This probabilistic approach allows to define a critical transport fluid velocity as the lower limit of the bulk fluid velocity by which no particle risk to settle. Similarly, one can define a critical settling fluid velocity as the upper limit of the bulk fluid velocity where every particle will sediment regardless of the initial conditions. With the described modelling of the particle movement and its associated statistical methods, it is possible to quantitatively estimate the spatial distribution of particles in any cross-section. For those particles that get trapped between the tool-joint and the borehole, it is then possible to estimate their size reduction by grinding, resulting from the rotation of the tool-joint on the borehole wall. The grinding process impacts the particle size distribution passed a tool-joint. By applying this method iteratively up to the annulus outlet, it is possible to estimate the particle size distribution of the drill-cuttings when they arrive at the shale-shakers.

Abstract In [1] we have developed a modified three-layer model for solid-liquid flow in horizontal pipes, which overcomes the limitations of previous mechanistic models. The steady-state model predicts the pressure loss, critical velocity, concentration profile in the heterogeneous layer, mean heterogeneous layer and moving bed layer velocities, and bed layer heights for each set of parameters. The steady-state model predictions show very good agreement with experimentally measured results in the literature. In this paper we extend the steady-state three-layer model to annular geometries and apply it to the design of open-hole gravel packing operations, in the typical parameter ranges of gravel packing operations for alpha wave placements. Alpha wave design is a key factor for successful gravel packing, and the models typically used are either based on small-scale experiments or are not specifically developed for gravel packing, e.g. cuttings transport models. In gravel packing the hydraulic configuration is slightly different. We explain how bed height is selected via coupling between the inner and outer annuli and from the outer annulus hydraulics. We investigate the effects of important parameters such as the slurry flow rate, mean solids concentration, wash pipe diameter, etc. on gravel packing operations.

Abstract This paper presents a novel approach to solving the 3D flow and displacement of completion fluids in the annulus formed by the gap between the outer wall of the casing and the wellbore rock face. Completion fluids displace each-other and follow a complex path promoted by rheology and density contrasts, casing movement and by the shape and orientation of the annulus. Muds and cement slurries often exhibit a yield stress, an additional challenge for optimal mud removal and cement coverage. This work extends previously published 2D models, to now capture fluid distribution and velocity profiles across the gap width in the 3D axial-azimuthal-radial space, at a lower computer cost than with conventional 3D CFD approaches. This gain is obtained by solving a 2D-only pressure equation for calculating the 3D annular flow, under the so-called narrow-gap approximation.

Abstract An Eulerian mixture model of the two-phase flow was used for cuttings transport simulation. The model was tested using experimental data for particles transport in pipes. Three types of problem statements were analyzed: steady-state flow, non-stationary flow in a short-length channel with periodic boundary conditions, and non-stationary flow in a long channel. Simulation of cuttings transport by Herschel-Bulkley fluid through an inclined 21-inch borehole/–6.5-inch drillpipe annulus was performed. All problem statements showed very close results, even for unsteady flow. These results demonstrated the applicability of 2D steady-state problem formulation for cuttings transport simulation. The unsteady flow was observed for an inclination of less than 20 degrees. Slow downward sliding of cuttings in the lower part of inclined boreholes was observed simultaneously with upstream dunes movement. Drill pipe rotation significantly decreased the cuttings concentration and pressure gradient, and shifted the maximum cuttings transport downward sliding rate from a 20- to 40-degree inclination.

Abstract We present a numerical investigation of laminar miscible displacement flows in narrow, vertical, eccentric annuli. This study is motivated by the primary cementing stage of oil and gas well production, where successful displacement of drilling mud is crucial for the well integrity and zonal isolation. The large number of characterizing parameters makes a complete description of such flows challenging. In turn, this means that the design of effective strategies for primary cementing is a difficult task. As a result the existing literature is mostly based on non-inertial Hele-Shaw models and experiments in narrow annuli, where the dimensionality of the problem is reduced. In this preliminary study, we run a series of three-dimensional numerical simulations, using a Volume of Fluid (VOF) method to capture the interface between the fluids. Both Newtonian and non-Newtonian fluids are considered, and a variety of different phenomena are observed, e.g. dispersive spikes, static layers, instabilities and secondary flows. The range of flow parameters used in the simulations are similar to existing experimental data to allow for a preliminary comparison. The results show qualitative agreement with the experiments and gap-averaged models.

Abstract Oil and gas well primary cementing operations involve pumping a sequence of fluids into the well, for example, cement along a circular pipe (casing) to remove (displace) in situ drilling mud. Cementing is vital to the implementation of zonal isolation and well integrity in the completion of oil and gas wells. The success of a cementing operation is largely determined by the displacement efficiency. There are several factors, such as rheological properties of fluids, geometrical specifications of the annulus, flow rate, and pipe movement, which can considerably affect the displacement efficiency. A casing rotation is generally believed to improve the displacement process, but without solid laboratory experiments to prove that such rotation is indeed effective. In this work, the influence of a pipe rotation on a displacement flow which consists of a yield stress displaced fluid is analyzed via experimental methods. A heavy Newtonian fluid (salt water) displaces a light viscoplastic fluid (Carbopol gel) in a long, inclined pipe. Our results show that the pipe rotation helps break up the Carbopol gel remained on the surface of the flow geometry, and eventually leads to an efficient removal of the displaced fluid above a critical rotation speed. The analysis includes measuring the propagation velocity of the leading front ( V̂ f ) for different parameters, such as the pipe inclination angle, the imposed flow velocity ( V̂ 0 ) and the rotation speed. The leading front velocity decreases as the rotation speed increases and it is found V̂ f ≈ 1.6 V̂ 0 . Three flow regimes are observed: slumping type, ripped type and effective-removal type.

Abstract In the drilling operations, it is common to have a stationary bed of the drilled cuttings in the high angle sections of the wellbore. The bed must be removed in the later stages before running the casing, or when it starts to cause high torque and drag on the drill string. The mere act of circulating drilling fluid, however, may not clean the well (i.e., critical flow rate and shear stress for bed erosion must be reached). In an effort to better understand the underlying mechanisms of bed removal process during hole cleaning, in this paper, we look at how the presence of a stationary sand bed affects the flow field in an eccentric annulus. Experiments simulating turbulent flow of water in an eccentric annulus with/without the presence of stationary sand bed have been conducted by using a 9m long horizontal flow loop (with an annular configuration of 95 mm ID outer pipe and 38 mm OD inner pipe). The flow loop was equipped with particle image velocimetry (PIV) system, which was used to collect velocity field data. The PIV data were then used to study the characteristics of the turbulent flow of water in the eccentric annulus. The velocity field and Reynolds stress profiles were analyzed in two planes, one perpendicular to the bed interface and off-center of the annulus, and the other along the center-line of the annulus. Experiments were carried out with the presence of two different height stationary sand beds and also without a sand bed as the control case. The extent to which the presence of the sand bed affects the flow appears to be a strong function of the bed height in the annulus. For a small bed height, deviation of the velocity field from the no bed case was slight. In this case, Reynolds normal and shear stress values were lower near the bed interface comparing to the annulus centerline. On the other hand, for a flow over a thicker bed, this behavior changed, and the flow became more uniform in the annulus (in terms of turbulence and mean flow properties). The results help in understanding the mechanism of bed erosion under constant pump flow rate. From the practical point of view, data presented here suggest that hole cleaning in an eccentric annulus progressively becomes more difficult as the bed becomes smaller. The results also explain why in long horizontal and extended reach wells often wiper trips are required for proper cleaning of the hole.

Abstract In this paper we present results from flow loop experiments with an oil-based drilling fluid with micronized barite as weight materials. The use of micronized barite allows using lower viscosity drilling fluid, providing non-laminar flow, which is advantageous for particle transport in near-horizontal sections. While transition to turbulence and turbulent flow of non-Newtonian fluids has been well studied both theoretically and experimentally, there are very few published results on the effect of wellbore wall properties on flow regime transition and turbulence. This is relevant because horizontal sections are often open-hole with less well-defined surfaces than a steel casing surface. We have conducted a series of flow experiments with and without cuttings size particles in a 10 m long annular test section using steel and concrete material to represent the wellbore wall of a cased and open hole section. In both cases the annulus was formed by a freely rotating steel pipe of 2” outer diameter inside a 4” diameter wellbore. Experiments were conducted at 48°, 60° and 90° wellbore inclination from vertical. The two materials result in different hydraulic behaviour without particles with stronger turbulence when using concrete wellbore wall material than when using steel casing. While there is negligible difference at low flow rates, at 0.8 m/s and below, there is an increasing difference as the flow rate increases and becomes transitional to turbulence. Hole cleaning is found to differ dependent on the wall material. However, the effect on hole cleaning is less clear than for the pressure loss.

As the tendency of the offshore oil industry is going deeper and further, the subsea pipeline is exposed under tougher condition combining lower temperature with higher hydrostatic pressure. The severe condition creates a challenge towards flow assurance, which often results in a high cost solution. Reducing the cost while providing a qualified insulation performance is of great significance to deepwater development. For ultra-deepwater beyond 1500m, single-wall pipe usually fails to meet the flow assurance requirements or requires a huge amount of insulation material. Pipe-in-pipe configuration can provide a good insulation performance but comes with a high cost associated. Sandwich pipe is a new concept composed of two concentric steel pipes separated by a cementitious composite annulus that provides a combination of high structural strength with thermal insulation. It is reported to be a promising alternative for both flexible and rigid conventional pipes in applications for long distance pipelines. In order to further investigate its feasibility in deep waters, a subsea production system with depth at 2200m was used as a case study for a comprehensive evaluation of insulation performance of the sandwich pipe, including both steady-state and shut-in working conditions. For a comparative study, scenarios using single-wall pipe (SW), pipe-in-pipe (PIP) and flexible pipe (FP) were also considered separately. The results showed that (i) sandwich-pipe performs better in steady-state but worse in between shut-in and the restart period (ii) sandwich-pipe with larger diameter performs better than it with smaller diameter. The reasons for the sandwich pipe behavior were discussed and suggestions to improve the performance are presented.

For un-bonded (sliding) Pipe-In-Pipe (PIP) systems, one of the main components is the centralizers (also called spacers). The main functions of the centralizers are to centralize the inner pipe inside the outer pipe, to transfer the loads between inner pipe and outer pipe and to safeguard the insulation material in the annulus from excessive compression during fabrication, installation and operation. Centralizers must also have good thermal insulation properties so that the heat loss is minimized. Different designs are now available for centralizers but the majority are based on two half shells which are bolted together. During fabrication, installation and operation, centralizers subject to different loads under which they are required to continue functioning properly. This paper provides an overview of centralizer design aspects and then focuses on the loading history during installation using reeling method. The main contributing parameters to centralizer loading during reeled installation technique are discussed and conclusions are drawn. It is believed that this will enable Pipeline Engineers to select the most appropriate material and design for centralizers.

When a drilling fluid column remains static over a timeframe of several years, the drilling fluid separates into different sediment phases due to gravity separation. These heavy sediments, entitled “settled barite”, are the cause of significant operational problems several years after drilling. An important problem caused by settled barite occurs when performing casing cut-and-pull operations during slot recovery and well abandonment: the casing is “stuck” due to the sediments in the annulus outside the casing. The consistency and rheological properties of the sediments determine how easily the casing is removed. In this paper, we report a preliminary study were we have artificially prepared gravity sediment phases for two different types of water-based drilling fluids; one KCl/polymer-based fluid and one bentonite-based fluid. By studying the rheological properties of the obtained sediment phases, we see that there are considerable differences between the sediments for these different drilling fluids.

Through the life-time of a production field in the offshore petroleum industry it is normal to drill several new wells for both production and injection purposes. The initial well template, either at the platform or at a subsea installation, has space for a fixed total number of wells. When this limit is reached an old well needs to be plugged and the well slot reused to allow new wells to be drilled. In order to re-use well slots and benefit from full diameter when constructing the new well, it is required to remove the tubulars in the upper part of the plugged well. The outside of these tubulars are normally in contact with cement or settled particles from shut-in drilling fluids. Removing the tubular through the cement or settled particle is always challenging and there is need for using new techniques. In order to address the dominating effects in these operations, down-scaled laboratory tests are performed. The experiments reported here are performed by pulling steel pipes out of a cemented annulus. The pipes used in the tests are down-scaled from typical casing sizes. They are either normal pipes, grooved pipes or pipes with and without collars. Two setups with different geometries are used. The first is selected to study the de-bonding effect from the cemented annulus and the mechanical friction that must be overcome to remove the pipe. The other setup is designed to show the effect of collars when pulling out the tubulars. Since most tubulars in wells have collars between each stand with extended diameter, this effect is important to consider when comparing laboratory results to field operations. Results show that the loosening force (de-bonding) and pulling force can be significantly reduced by manipulating the pipes with grooves prior to pulling them out. Further, the results show that the most significant resistance when pulling the tubulars are caused by the collars outside the pipe. It is also observed that the effect of collar is significantly reduced when the pipe is grooved between the collars. In total these results provide improved understanding on the dominating effects when pulling pipes from packed wellbore annulus.

Preflushes are often used as part of the sequence of fluids pumped in primary cementing. Usually two functions are served by preflushes: I) to wash the drilling fluid ahead, by a combination of turbulence and chemical reaction; II) to provide a chemically compatible spacer between the lead slurry and the drilling mud. In some cases a wash precedes a spacer, but often only a single preflush is used. We consider well parameters typical of surface casing cementing in North Eastern British Columbia. Using a two-dimensional model of annular displacement flows, we show that the wash concept is flawed. In particular, in a sequence of simulations varying from intermediate density to low density we show that the wash progressively advances ahead of the lead slurry, channeling rapidly up the wide side of the annulus. Even when fully turbulent, it is ineffective at displacing mud from around the annulus, invalidating the motivation of chemical cleaning through contact time. Furthermore, the advance along the wide side of the annulus drains the volume of fluid separating the cement from drilling mud. Thus, the idea that the wash provides a barrier between slurry and and mud is invalid.

One current methodology for Carbon Capture and Storage (CCS) involves pumping carbon dioxide (CO 2 ) into a depleted oil and gas reservoir, usually via an existing well. Permanence of the storage in this case relies on the integrity of the reservoir and also the avoidance of leakage at the points of entry. Two different cementing procedures are involved in the latter problem: primary cementing and squeeze cementing. Here we consider how to track the interface between two fluids during primary cementing. The main idea is to exploit the density difference between successive fluids pumped in order to design a tracer particle to sit at the interface. Although apparently trivial, such particles must also overcome strong secondary flows in order to remain in the interface. We provide a proof of concept analysis of this situation assuming the displacement involves laminar flows of two Newtonian fluids in a narrow vertical annulus and demonstrate its feasibility.